1. Field of the Invention
This invention relates generally to wastewater treatment and, more particularly, the invention relates to removal of water-insoluble organic contaminants such as oil and grease from wastewater streams.
2. Description of Related Technology
The decontamination of acidic streams such as waste streams containing substantial concentrations of oil and grease or other substantially water insoluble organic contaminants has long been a problem. While separation methods utilizing sorbents such as organophilic clays (sometimes referred to as "organoclays") have found great success in removing organic contaminants from aqueous waste streams, such methods have not been believed to be useful for use with highly acidic streams.
One commercially successful system for removing a wide variety of organic contaminants utilizes a sorbent comprising an organoclay, such as a previously prepared reaction product of a quaternary ammonium salt and a smectite-type clay, such as sodium bentonite, for example, generally by passing the contaminated stream through a packed or fluid bed of the sorbent.
Such clays are known to have a plate-like structure that selectively adsorbs low solubility organic compounds, causing the clay structure to swell to accommodate further adsorbed contaminants. Such sorbents are typically utilized in a mixture with a suitable diluent having a similar density, such as anthracite coal, to prevent premature caking of the bed and consequent breakthrough of the influent stream.
Such systems are described, for example, in Beall U.S. Pat. Nos. 4,473,477 (Sep. 25, 1984) and 4,549,966 (Oct. 29, 1985).
Beall U.S. Pat. No. 4,517,094 (May 14, 1985) teaches the utilization of a secondary separating means such as a packed bed of activated carbon and/or air stripping means for removing substantial quantities of low molecular weight components of the organic contaminants that may remain in the effluent from a primary sorption stage utilizing an organoclay sorbent.
Such systems have been utilized with great success in treating processor waste streams such as boiler feedwater, metal casting waste streams, effluents from wood treatment plants and electroplating or paint stripping installations, and others. However, organophilic clay sorbents have not been utilized for the removal of water-insoluble organic contaminants such as oil and grease from waste streams having very low pH levels. This prejudice in the art resulted from a belief that at a pH of about 3 or less acid present in such streams will attack exposed edges of the clay structure and leach out the aluminum octahedra of the clay, thus destroying the clay structure, leading to breakdown of the water treatment system.
This leaching of Al.sup.+ from clay is utilized commercially to produce a family of materials called bleaching earth. These materials are utilized in decoloring of vegetable oils. It is well known in the art that when these clays are acid activated the structure is so substantially altered that the interlaminar space is collapsed and is no longer accessible. Since the invention relies on this interlaminar space it was thought that such acid conditions would also render the organoclays ineffective.
One type of hydrocarbon-contaminated acid wastewater stream that requires removal of substantial quantities of contaminants is the acid wastewater return stream which is created by acid oil well refurbishment processes. In such processes, large amounts of strong acids, typically mixtures of hydrofluoric acid and hydrochloric acid, are utilized to refurbish oil well production lines, both offshore and onshore, on a periodic basis. The task of disposing of contaminated returns from such refurbishment processes has been a difficult one, which has met with only limited success. According to one prior art decontamination method, oil and grease are skimmed off the return stream by flotation, and the contaminated low pH effluent is then transported via pipeline to a dry well for burial. This procedure is no longer permissible, as governmental regulations strictly regulate the composition of acid waste streams that may be disposed of in the environment.
The acidic wastewater return streams generally have an extremely low pH of 3 or below, typically 2 or below, and often in the range of about 0 to 1.5. Such streams generally have oil and grease contaminant concentrations of at least about 200 ppm, generally in the range of about 10,000 ppm to about 20,000 ppm after gross separation of oil and grease by flotation, and may have oil and grease concentrations of up to 50 percent (or more) if flotation separation is not utilized.
The inability to effectively remove water-insoluble hydrocarbon contaminants from acidic wastewater returns has resulted in great effort and cost, as well as production downtime due to contamination entering production flow lines.